Process for dewaxing hydrocarbon oils



Dec. E4, 937. E. PETTY PRocEss FOR DEWAXING .HYDRocARBoN OILS FiledApril 14, 1.933

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Patented Dec. 14, 1937 UNITED STATES PATENT OFFICE Earl letty,Hempstead, N. Y., assignor, by mesne assignments, to Sun Oil Company,Philadelphia, Pa., a. corporation cf New Jersey Y Application April 14,1933, Serial No. 666,099

6 Claims.

My invention relates to a process for dewaxing hydrocarbon oils and moreparticularly to a process of dewaxing in which pressablewax crystals areproduced by chilling wax-bearing-distillates from crude oil.

This application is a continuation in part of my co-pending applicationentitled Process of xligzvsaxing oil, Serial No. 624,968, filed July 27,

Heretofore, to produce pressable wax distillates from crude oil itrequired a high degree of fractionation and a very careful selection ofthe pressing fraction. 'I'his pressing fraction usually had a boilingrange of from 450 F. to 675 F. 10 m/m Hg. absolute pressure.

One object of my invention is to provide a methodv of dewaxinghydrocarbon oils in which the fractions which can be dewaxed by pressingare extended to include oils of a boiling range up to '725 F. to '750 F.10 m/m Hg. absolute pressure.

Another object of my invention is to provide a method of chillinghydrocarbon oils which will greatly improve the formation of pressablewax therein. Y

Another object is to produce a more oil-free wax crystal by improvingthe conditions under which crystallization is conducted.

Other and further objects of my invention will 30 appear from thefollowing description. f

'Ihe accompanying figure, which is to be read in conjunction with theinstant specification and which forms part thereof, shows a diagrammaticview of an apparatus capable of carrying out my invention.

In general, my invention consists of blending, under pressure, apredetermined amount of hydrocarbon such as propane with the wax bearingoil. It is to be understood that throughout this 40 specification bypropane is meant any of the low boiling hydrocarbons which may exist ina liquid state in the normal temperature range by the imposition ofsuper-atmospheric pressure.

Commercial propane, for example, is liquid within 45 the normaltemperature rangeat pressures between 80 and 120 pounds per square inchand contains at least 60% of pure Cal-Ia. At atmospheric pressure itboils at approximately 45 F.

and solidies at about -300 F. These later 50 characteristics indicateanother contributory and complimentary characteristic of this diluent,viz a low viscosity. The viscosity of gasoline or naphtha normally usedas a diluent in connection with Adewaxing at temperature of C. is anaverage of .00690 C, G. S, unit., whereas propane has a viscosity at thesame temperature of .00125 C. G. S. unit. This low viscosity indicateshigh freedom of movement and velocity of the molecular structure and hasdefinitely proven to be very advantageous to crystallization, when it ispresent as a diluent. The other characteristic of low temperature ofboiling makes it possible to remove the propane as thecrystallizationprogresses. The removal of this diluent has the effect ofaccelerating crystallization by concentrating the amount of oil in themother solution. In other words, the crystal is formed and cul-V turedduring the first part of the cooling bythe dilution and low viscosityeffect of the propane. Then the increased concentration of the oil andincidental refrigeration eiect produced by allowing the propane toevaporate produces the final Wax crystal. These above complementary andcontributory physical eiects are accomplished by the following chillingprocedure. The blend is made at approximately 80 to 100? F. The chillingis divided into two stages, viz, 1st, in- `direct heat exchange toapproximately 30 F., and

2nd, by evaporation of the propane and the incidental reduction oftemperature to as/low as -30 F. In the first stage the blended mixtureis passed under pressure through precoolers in order to chill the sameby indirect heat exchange.

The precooled mixture is then passed into theV evaporator-crystallizerfor concentration by the removal and evaporation of the propane andincidental refrigeration or cooling. This is accomplished by reducingthe pressure on the evaporator and results in the evaporation andremoval of substantially all the propane. The effect of the propane uponthe wax during the pre-cooling is as a diluent to reduce the viscosityofthe solution and accelerate the crystallization. The final chilling,incidental to evaporating the propane, is such that a desirable waxcrystal is developed due to increased concentration of the oil in thesolution, producing a wax of improved filtering quality. (See co-pendingpatent application 632,- 278, Sept. 9, 1932.) This effect enables me, bythe practice of my process, to extend the range of pressable wax bearingoils, or to increase the rate of filtration, and reduce the oil contentofY the wax. The propane from the evaporator isV recovered for re-use.The chilled oil containing the wax crystals and substantially freeoi:`propane is then passed to a CO2 stripper tower 50 where CO2 vapors areexpanded into tower lilly counterflow to the chilled wax ydistillatebefore4 it is passed to lter press. In the tower 50, by the vstrippingstep, the final traces of propane are removed and replaced with CO2vapors. The oil which Vis recovered from the pressing operation, at avery low temperature, is passed in heat exchange with the incomingmixture as the cooling medium although it is understood that any othersuitable refrigerant may be employed for the indirect heat exchangestep. The oil is then passed to a pressure evaporator to insure thecomplete-removalof"propane andl CO2 therefrom, nally stripped by steamto remove 'the last trace of any of the volatile products, and thenpassed to storage and further processing.

If desired, the processbouldbe modifiedby combining the steps performedin the stripping tower .and evaporator by passing C052 vapors directlyinto the oil transfer line yfro eX- changer to the evaporator, indirectinto the evaporator, thereby eliminating 'the stripping v the blendingtank *4, inlfwhich a'thor'ou'gh mixture ofthe bill-tobe dewaxedwith'the" propane, is

effected'' It" is: toV be-'understood 'that suitable agitatin'g meansmaybe vprovided in 'theblending tank. -The nri'xtur'e' orVV solution is"pumped throughf valved line" 9 by pufmpilll, through heat exchangersHfThese-hein;VVVV exchangers may be of any suitable type.The'drawirigillustrates a diagrammatic viewof scraped surf ace heat exchangers.A -The "solutionlisfchilled in r heat exchangers andlpassesIthrough line`V |2 into the evaporatory crystallizenil 3,'ingwhich thepressure is 'reduced to fallowthe propane to* evaporate to l secure'additionarand" runner smiling;- AIf, uesired, propane Ymay be passedthrough line |'4 and pumped "by I5y through line" I@ iht'o the to secureadditional and evaporato'r crystallizer further cooling." 'f

-The Igaseousl propane leaves lthe evaporator crystallizer I 3f throughline V| 1 `and""'pressure reducing valve H1 and mayvv be recovered byVany suitable means.'-" Separator I8 is providedto in surethat'n'doilis"'carried'outv of the system, the oil freturningthroughlie |9.l Pump|5is adapted to takesuction"'throughf'valve :1ine20jfor reing pressablewax'erystals is Ywithdrawn'`from evaporator Vcrystalliz'er*|3throughvalved; line 2'! by pump 55,*valv`e |-'22 being? closedgandpas'sesthrough line |l2| into "CO2 strippen 50.5; CO2 vapors from cylidersSlvor" 52Y are passed: into this stripper through'pipe |75| 'andpipe |52controlled by valves v|53 and |54iand dueto the partial 'pressureeffecttheremainder ofthe propane is removed?" Thepropanev7 andVCOzvapors are taken'of :throughvapo'iline 53 and pump 54'to becompress'edan'd recovered.- The chilled stripped liquid' is with'drawnirm" the tower 50'Y through line'f-Zlq;A by means of pump-*55a by whichit is fed'tothe iilterV or pressing system. (It is notintended'tofusethe COzasa refrigerant at this stag'L-'flfhe' tower wouldfbelcarefully' insulated nd'the 'amoun't' of CO2 vapors used 'would notremove heat, and rthe effect of these vapors wduldffbefto remove the'entraihed propane and thereby give slight refrigeration effect fromevaporation of propane, due to partial vapor pressure eiect.) arearranged in parallel.

The Wax leaves the lter presses through lines 28, 29 and 30 andpassesinto wax receiver 3| which is provided with a tting 32 through which areduced pressure may be placed on the Wax receiver to evaporatethereiromf all tr-acesiof volatile'propane and/or CO2.` The cold dewaxedoil Yleaves the filter' presses through lines 32, 33 and .3"` throughline 35, and is pumped by pump 36 through 'th'e'heat exchangers Il tochill the in.- coming solution. The oil leaves the heat exchangers v||through line 39 and passes into stean'istripper 45. The dewaxed oil,freed of the solvent, is than pumped by pump 48 into storageltank 48,Recycle with the undewaxed oil may be'practiced'to reduce cold test andthickness of'rnaterial being dewaxed by diverting a portionpf thedewaxed oil in line 39 thro-ugh line 44 by means of pump'45 or throughlineMc (or the wax-distillatetmayb 'diiutedfasfonvea tionally practiced,with glas` oil or' kerosene) "The rlter presses I:maybe ofthe'conv'entional type or may be special .continuous'orjbatch type Itwill be seen that I have accomplished the objects of/r'nyinvertion. amvenabledt pro'- duce pressable wax from distillates of a greater boiling"range'. By my methodiof' chilling; I 'am Y enabled toproducerpres'sa'ble waxfwhereiit" has been -impossible heretofore' tordq so; 'and' alsoto produce 'ag'greater' amount of pressable wax for' a'given"fraction, enabling the complete dewaxing thereof. An increased"crystal'ff'formation is achieved by the use of propanefas a 'diluentaccompaniedbythe manner inwhi-ch Ichill the solution. I preclude 'theldanger-:of flirein the pressroom byr keeping itfinan atmosphere ofmetgas'm. .l y It will be understood that certain features,sub-combinationsand operationsy arei of utility and maybe "employedwithutrreference to any other features4 and A'sub=combinations. iscontemplated by and is within the scope-of 'my claims. ItY is furtherobvious that various. changes may be made in detailswithin the'scope ofmy claims without departing from the spirit of my invention. It' is,Ythereforefto be understood that my'invent'ion isv not to be Ylimited t0-the specific details shown anddescribedi` Filter presses 22, 23 and 24,as shown,

It willbe'un'derstood,further, that', while I ed hydrocarbons expandedto 'chill the oiland Y the wax then removed from the oil, the step ofstripping the chilled oil ofr residual normally gas# eous hydrocarbonsafterthe expansion 'step byv means-of` an inert gas lower boiling thanthe normally gaseous hydrocarbons.

'2. A method'of'rdewaxing hydrocarbon oils including'the-steps of mixingthe oil to be dewaxed with liquefied normally gaseous hydrocarbons,chilling thevoil by evaporating normally gaseous hydrocarbons mixedtherewith, removing the residual hydrocarbons from the chilled oil bystripping with carbon dioxide in a stripping zone, and then dewaxing theoil.

3. A method of dewaxing hydrocarbon oils including the steps of mixingthe oil to be dewaxed with liqueed propane, cooling the mixture byindirect heat exchange, chilling the cooled oilV by evaporating thepropane, removing'the residual hydrocarbons from the chilled oil in astripping zone by stripping the oil with a gas lower boiling than thepropane and then dewaxing the oil.

4. A process of dewaxing hydrocarbon oils including the steps of addinga low viscosity normally gaseous hydrocarbon diluent to the oil tofacilitate crystallization of wax in the oil during a pre-cooling stage,chilling the diluted oil by indirect heat exchange in a rst chillingzone to initiate crystal formation, evaporating substantially all of thelow viscosity diluent from the chilled oil in a second zone of chillingto concentrate the amount of cil in the mother solution and secure nalwax crystal development, then removing the residual diluent from thechilled oil by stripping with an inert gas lower boiling than thediluent and mechanically removing the wax from the oil.

5. A method of dewaxing a hydrocarbon distillate of boiling range from450 F. to 750 F. 10 m/m I-Ig. absolute pressure including diluting theoil with low Viscosity normally gaseous hydrocarbons under pressure andin the liquid phase and in sufficient quantity to serve as anaccelerator of crystallization by low viscosity effects during apre-cooling stage, cooling the diluted oil by indirect heat exchange toapproximately 30 F., removing substantially all the diluent from the oilby evaporation which by incidental physical efrects results in coolingand co-incidental concentration of the oil in' the mother solution andproduces a further developed wax crystal substantially oil free, carriedin oil, then freeing the oil of residual diluent by stripping with anormally gaseous, non-iniiammable' material of a lower boiling rangethan the diluent, and mechanically removing the wax crystals from theoil.

6. A method of dewaxing hydrocarbon oils including the steps of mixingoil to be dewaxed with a liquefied, normally gaseous hydrocarbonVdiluent, then chilling the mixture and increasing the concentration ofthe oil in the mixture by stripping the diluent hydrocarbon from the oilwith a normally gaseous, Ynon-inilammable ma` terial of a lower boilingrange than the diluent and removing the wax from the oil.

EARL PET'I'Y.

